Do flea bites swell up?


Flea bites can swell up. Typically this occurs during the delayed reaction, 12-24 hours after the flea feeds. The edema (swelling) can accompany a welt-like lesion called a papule.


Edema & Flea Bites

Initial Reaction

Shortly after a flea bites, the nearby affected skin begins to elevate. The slightly raised lesion is called a wheal. Swelling (edema) may accompany the early reaction.

Delayed Reaction


12-24 hours after the bite, the wheal is supplanted by a papule, which is a small, itchy, welt-like lesion. Some individuals experience a rash with numerous tiny papules, called maculopapules. Redness and edema can occur with both of these lesion types. Occasionally, the papule’s center develops a vesicle (tiny fluid-filled sac).


In extreme cases, delayed reactions can become blisters (bullous reactions). Fluid accumulates under the skin, eventually combining and swelling into a large blister (bulla).

Inflammation from Scratching

Scratching a flea bite causes inflammation and increases the sensitivity of nerves in the area. While not necessarily swelling, the skin can become inflamed.

Scratching a bite can also break open the skin and release fluid. This can trigger secondary bacterial infections. Infected bites can then fill with pus and resemble pimples.


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